Vehicle emissions: Issues and workarounds for various monitoring conditions

In March 2022, within a broader-treatment post on automobile owners’ rights to repair their own vehicles, I briefly introduced the topic of the on-board diagnostics (OBD) port, used to monitor (and in some cases, as you’ll soon see, manipulate) vehicle status information:

I dove into the topic in greater detail earlier this year, within the teardown of an OBD-II scanner:

Here again, by means of (re-)introduction, is the summary definition from Wikipedia’s entry:

On-board diagnostics (OBD) is a term referring to a vehicle’s self-diagnostic and reporting capability. OBD systems give the vehicle owner or repair technician access to the status of the various vehicle sub-systems. The amount of diagnostic information available via OBD has varied widely since its introduction in the early 1980s versions of on-board vehicle computers. Early versions of OBD would simply illuminate a malfunction indicator light (MIL) or “idiot light” if a problem was detected, but would not provide any information as to the nature of the problem. Modern OBD implementations use a standardized digital communications port to provide real-time data in addition to a standardized series of diagnostic trouble codes, or DTCs, which allow a person to rapidly identify and remedy malfunctions within the vehicle.

Likely unsurprisingly, at least to some of you, OBD monitoring finds use for (among other things) assessing a vehicle’s emissions status, including but not limited to factors such as the catalytic converter’s effectiveness and whether (and if so, to what degree and with what results) the vehicle’s periodic emissions auto-checking has completed. Over time, I’ve gotten more adept at this particular OBD monitoring “angle”, out of necessity and aided by equipment acquisitions.

As background: my wife and I are blessed to own two more vehicles (both of which, along with my 2008 Volvo XC70 primary “wheels”, came to the marriage via yours truly) than fit inside our two-car garage. They’re both rare “classics” (IMHO, at least), and all three cars are low mileage and in great condition, thereby explaining my reluctance to part with any of them. One “extra” is a 2001 Volkswagen Eurovan Camper (a Winnebago conversion, not the Westfalia model):

The other’s a 2006 Jeep Wrangler Rubicon Unlimited, complete with both hard and soft tops:

Since our homeowners’ association (HOA) is a stickler for vehicles permanently parked on the street or in driveways, we’ve been storing the two “extras” under thick weather-resistant covers at a nearby outdoor lot.

The Eurovan Camper was my “moving van” for pets (two dogs and two cats) and other important possessions when I relocated part-time (at the time) from California to Colorado. Later, about a decade ago, I took a road trip back to CA, because the vehicle was still registered there and was due for periodic emissions testing, with passing as a condition of renewal.

Just outside Reno, NV, and less than an hour east of my destination, I stopped to fill up the gas tank. Only a few miles further down the road, the “check engine” light in the dashboard went on (although the engine thankfully remained running smoothly) and stayed on. This was a problem, particularly considering the primary motivation to make the road trip in the first place. Emissions testing requests are summarily rejected, at least in both CA and CO, if the “check engine” alert is illuminated at any point during the tests, reflective of OBD Diagnostic Trouble Codes (DTCs) (not to mention whatever foundational issue(s) had activated the alerts).

The local mechanic told me that I’d probably gotten some “bad gas” and that I just needed to drive the VW around for a while, at various speeds both steady and time-variant, to:

Burn through the “bad gas” (I’d then replace it with hopefully higher quality stuff), and
Allow the vehicle’s various diagnostics tests to run again and issue an OBD “all-clear”.

He explained these tests (commonly referred to as a “drive cycle”) auto-ran under different operating conditions, as well as after varying numbers of ignition key start sequences, therefore the need for driving-behavior diversity. I’d honestly (and likely ignorantly) not heard of such a thing before, but he seemed like he knew what he was talking about, so I followed his instructions with as much driving variety as I could muster. And he was right; a couple of days later the “check engine” light went off and stayed off, and I still had time to get it emissions-tested (it thankfully passed) prior to the deadline for my return to CO.

Fast forward to last year. As previously mentioned, I store the vehicles in an outdoor lot. And they’re due for emissions testing (an every-two-year requirement, complete with time on a dynamometer, given their ages) on alternating years. I’ve also historically kept their batteries disconnected when parked, since I don’t have AC outlet access for trickle chargers and the batteries would therefore otherwise slowly-but-surely drain. So, every year, I go to the lot, remove both vehicles’ covers, hook up their batteries and jump-start as needed, reorder them:

and drive the now-in-front vehicle a couple of miles down the road for emissions testing.

Last year (why it took until then, since I’ve been doing this procedure for nearly a decade now, is something I still haven’t sorted out), that pattern no longer panned out. The guy at the testing site told me not that the Jeep had failed emissions, but that the testing hadn’t completed. He then handed me a report, stamped “Incomplete” at the top, along with a pamphlet from the state (apparently this happens often), which was informative. A few report excerpts:

Readiness Monitors:

Catalytic Converter: Ready
EGR System: Not Supported
Evaporative: Not Ready
Oxygen Sensor: Ready
Oxygen Sensor Heater: Not Ready
Air System: Not Supported
Air Conditioning: Not Supported
Heated Catalyst: Not Supported

 The vehicle’s OBD system has not yet completed its self evaluation. The OBD system must be working properly and the supported readiness monitors set to “Ready” before attempting another OBD test.

 Readiness Monitor Information

 There are several readiness monitors that allow the vehicle’s OBD system to identify potential emissions problems. The following tips will help ensure the vehicle’s OBD system is prepared for the emissions inspection:

Make sure the Check Engine light is not illuminated, while the engine is running.
If this vehicle recently had emissions-related repairs, or if its diagnostic trouble codes were cleared, or if its battery was disconnected, then the vehicle must complete a drive cycle for its readiness monitor status to be set to “Ready”.

 You can find a list of different vehicle manufacturers’ drive cycles at colorado.gov/cdphe/drive-cycles [editor note: I can’t actually find them there, only general information, although maybe I overlooked something]. For most vehicles, driving it for a few days in both city and highway conditions will set the readiness monitors. Contact your vehicle manufacturer, a qualified service technician, or a State Emissions Technical Center for more information.

And here are scans of the various pages of the accompanying pamphlet (yellow highlighter markings on page 2 are courtesy of my new testing-center friend):

Remember how I earlier mentioned that I’d kept the vehicles’ batteries disconnected when parked, to prevent them from draining? Apparently, some of the discharge was caused by battery-backing up, whenever the vehicle wasn’t running, whatever volatile memory (SRAM, I assume) was storing the most recent drive-cycle results data. No battery = no more data.

The Jeep, as I’ve already mentioned, had been sitting outside essentially unused for many years, always covered (and with tires elevated above the ground, keeping them in good shape too) but still exposed to the elements (and rodents) from underneath. I was concerned about (among other things) belts and hoses that may have dried and cracked, not to mentioned chewed wiring, so my first step was to take it to a local mechanic for a once-over. Good news: it was still in great shape. Bad news: he couldn’t get all the drive cycle tests to complete.

So, I drove it around for a few days, then took it back to the local mechanic, who did another OBD scan (I hadn’t yet bought my own unit) and confirmed it still hadn’t completed all the tests. The “oxygen sensor heater” test was the one still “stuck”, and I’d done research indicating that the root cause might be a wiring fault covered by the manufacturer under lifetime warranty, so my next visit was to a nearby Jeep dealer’s service depot. Fortunately, there was one mechanic there who was old enough to have had experience with 2006-era vehicles, and he assured me that I just hadn’t yet covered the exact driving scenario necessary for it to run. Finally, it reported “ready”, and my return visit to the emissions testing site was also successful.

Fast forward to this year. It was now the Eurovan Camper’s turn in the emissions testing spotlight. Remember this quote from my September OBD-II scanner teardown?

The OBD-II scanner that I currently own (for reasons that I’ll save for another blog post another day) is an Autel AutoLink AL519, which I bought last November from an eBay retailer for $59.98.

This is the “another blog post, another day” I was alluding to.

Two years ago, when driving the vehicle away from the center after a successful test, the “check engine” light had turned on, so I knew I’d need to be proactive this time. After a few dead-ends, I eventually found a local (excellent) specialty repair shop, who did a full refurb on the vehicle, both mechanically and cosmetically. I pulled away armed with guidance to drive around for a few days to give it a proper drive cycle test opportunity and clear out any remaining “old” gas along with the fuel-system cleaning additive he’d put in, then refill it with “fresh” premium fuel before visiting the emissions testing center.

Two days later, while still driving the Eurovan Camper around on its “old” gas, the “check engine” light came on. When I got home, I pulled the OBD reader out of its box, updated its firmware and database to the latest-and-greatest, and plugged it into the OBD port in the underside of the steering column. Here’s what I saw:

Back to my mechanic, who confirmed the failed rear oxygen sensor diagnosis. He also installed the dashboard-mounted, OBD-based ScanGauge II that I previously purchased at his suggestion:

which monitors vehicles’ status both in additional detail for gauges and even lower-precision warning lights already in the dashboard (such as engine temperature and RPM, and battery and alternator status) and over-and-above information (transmission temperature, for example, particularly important in a heavy vehicle such as this, and gas mileage).

I left the mechanic’s shop with the “check engine” light off again…and the next day it was back on. Fortunately, the ScanGauge II, like my AutoLink AL519 albeit more conveniently, also supports not only reading and decoding but also clearing OBD diagnostic trouble codes. A few front-panel button presses and the “check engine” light was back off. At that point, with the registration-renewal expiration date looming, I figured it was time for me to fill up the van with fresh fuel and get down to the testing center. On the way there, the light came back on, and it also re-illuminated on the way back home afterwards. But in-between, the vehicle passed.

I’m still not sure why I’m getting intermittent P0140 DTCs, especially since the vehicle’s running smoothly and per its test results isn’t exceeding any emissions test limits. My best guess at this point is faulty wiring; I’ll be taking it back to the shop shortly for another diagnostics scrub. But thankfully, I’m “good” from an emissions perspective for another couple of years, in no small part thanks to the assistive knowledge and gear I’ve accumulated, along with the regulatory requirements that have ensured my access to the vehicle information I needed to sort out and resolve the issues I came across. If you’ve encountered and dealt with similar situations in the past, I look forward to hearing about them in the comments.

—Brian Dipert is the Editor-in-Chief of the Edge AI and Vision Alliance, and a Senior Analyst at BDTI and Editor-in-Chief of InsideDSP, the company’s online newsletter.

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